I'm planning on buying a head to use as a template for fabricating a turbo manifold. My 225 is a '69. I'll also keep this head as a spare. Should I get a later head with the hardened exhaust valve seats or is there some disadvantage to the later heads (pollution control etc)? Also, what year did they start using the hardened valves? Is that the same year that they started using the smaller spark plug holes, and if not is there some other way of identifying these heads? How much should I expect to pay? Thanks for any advice.

Bob D


BBobbias@aol.com

The induction hardened valve seats started in 1972 for SL6 engines. By 76, all heads changed to the "Peanut plugs" and all these have induction hardened seats. The only dis-advantage to these "later" heads is extra weight, mostly due to a air pump passageway cast into the head.

If you are going to build a "performance SL6 head, use a 68 and later head having the revised combustion chamber for a more complete burn. I would bet that you will only find the mid 70s and later heads in your area so you may as well get one of those "small plug" units.
DD

Please tell me (us) more about this "revised" combustion chamber. I know they changed chambers over the years but I don't have any reference or learning material about it.

cfield@ll.net

In 1968 Mopar changed the shape of the SL6 combustion chamber. They added some metal around the exhaust valve to get rid of a "cold spot". There are a few other small differences such as a more pronounced step right under the spark plug. The "cc" volumn of the chamber did not change.

This more efficient chamber design was used from 1968 on. If you are going to do any kind of serious SL6 cylinder head work, do it on a 68 an later head. I will try to dig-out a photo and get it scanned & posted later.
DD